Direction finding receiver circuit



April 27, 1937. Y w. KUHLEWIND 2,078,765

I DIRECTION FINDING RECEIVER CIRCU IT Filed Jan. 27, 1936 INYENTOR. WALTER KUHLEWIND Patented Apr. 27, 19 37 PATENT OFFICE DIRECTION FINDING RECEIVER. CIRCUIT Walter Kiihlewind, Berlin, Germany, assignor to Telefunken Gesellsehaft fiir..-Drahtlose Telegraphic in. b. H., Berlin, Germany, a corporation of Germany Application January 27, 1936, Serial No. 60,897

In Germany January 12, 1935 5 Claims.

The present invention relates to a receiving circuit having both a directional antenna and an auxiliary antenna. More particularly the invention relates to means for avoiding the detun- 5 ing of directional antenna circuits.

Stations for reception of direction finding signals at minimum intensity suffer the disadvantage that, due to the influence of .the surroundings,, the signal cannot be reduced to a 10 desired minimum. A sharp minimum would be obtained if the directional antenna such as the frame, for instance, were free in space. This ideal condition, however, can practically not be obtained. Ordinarily, the directional antenna 15 is more or less surrounded by reflecting objects causing, despite the setting of the antenna to the minimum, a reception to be present owing to the reflected radiation turned at reflexion in the plane of incidence. Furthermore, any frame 20 antenna acts as a small untuned antenna due to its ground capacity.

In order to compensate these undesirable effects, a small non-directed, aperiodic auxiliary antenna has heretofore been associated with the .25 directional antenna and the phase and amplitude of the additional auxiliary antenna is dimensioned by means of circuit elements in such a manner that the disturbances due to reflected radiations are compensated, thus obtaining a 30 sharp minimum of direction finding signals.

However, this method is found to require the taking of further precautions, since detuning of the frame circuit occurs especially when the coupling between frame circuit and auxiliary an- 35 tenna is made variable. Apparatus of this kind is difficult to handle in practice.

As is known, decoupling between frame circuit and auxiliary antenna circuit can be obtained by interposed amplifier stages. These arrangements 4 were found to be successful, but they require additional circuit elements, which are more or less complicated and unsatisfactory.

It is also known that, in order to compensate the detuning, a variometer may be placed in the 45 frame circuit whose setting takes place autotively free from impedances. All matching and compensating means are placed in Circuits between frameand auxiliary antenna.

The direction finding receiver circuit according to the invention and utilizing a, directional antenna anda linear auxiliary antenna is characterized in that for the suppression of reaction upon the directional antenna circuit at variation of the energy transmitted from the auxiliary antennato the directional antenna, an aperiodic circuit, or. intermediate circuit highly detuned with respect to the receiving wave, is provided, witha constant inductive or capacitive coupling to the directional antenna circuit, and with variable inductive, or capacitive coupling to the 15V auxiliary antenna.

As directional antenna there are preferably used frame antennae or goniometer antennae.

In most cases, the intermediate circuit comprises an inductance fixedly coupled to the tuning circuit of the frame and a number of condensers more or less independent of each other. By suitably dimensioning and connecting the condensers it is accomplished that despite the varying coupling between auxiliary antenna and intermediate circuit, the effective capacity of the intermediate circuit remains constant.

My invention will now be explained in further detail, reference being made to the accompanying drawing in which Figs. 1 to 4, inclusive, show diagrammatically four illustrative embodiments.

In Fig. 1, item I represents a receiver circuit of a frame antenna including an inductance L and a capacity C. Item II shows a small preferably linear, untuned auxiliary antenna. The intermediate circuit III with inductance J and one or several capacitances K1, K2 and K is the connecting link between frameand auxiliary antenna. The inductance L of the frame circuit I is fixedly and unvariably coupled to the inductance J of the intermediate circuit III.

The coupling between circuit III and auxiliary antenna II is obtained by a double difierentialcondenser K1, 2. This condenser is so constructed that the resultant capacity at the coil J is the same for each position of the condenser. For the purpose of correcting eventual small deviations, a further condenser K is provided whose capacity approximately corresponds to the capacity of the auxiliary antenna. A switch U is connected with the setting device of the condenser K1, 2. This switch has contacts T1 and T2 by means of which the direction of the current passing from the auxiliary antenna through the 5 coil J can be reversed. Since the natural wave of the circuit III is constant at each position of the condenser K1, 2, and the coupling between intermediate circuit and frame circuit an invariable one, this arrangement affords control of the requirement of the auxiliary antenna and variation of the direction of the current in the coil J without detuning the frame circuit I.

In Fig. 2 identical reference characters relate to the same circuit elements. Circuit I remains unchanged. Only circuit III and its coupling to the antenna II have been modified. Auxiliary antenna and ground are placed across two variable condensers K1, and K2, at the coil J fixedly coupled to the frame circuit coil L. Each condenser has two stationaryand one rotatable plate system. The rotatable systems are mounted on a common shaft. The variable condensers are so dimensioned and adjusted that the total capacity and hence the natural wave of circuit In remains always constant. To correct eventual small deviations, a further condenser K is placed in the ground connection. At the right handor left-hand turn of the rigidly coupled condensers K1 and K2 the current of the auxiliary antenna passes through coil J either in the one or the other direction. At the center position the resultant current through the coil J is approximately equal to zero.

In Fig. 3, the intermediate circuit consists of two different parts. The coil J1 having a center tap forms with condenser K1 the one part. The value and direction of the current in coil J1 depends upon the setting of the condenser K1; At such coupling, detuning of the tuning circuit of the frame is unavoidable. In order to compensate the detuning a further part J2, K2 is provided likewise coupled to the frame circuit I. The two condensers K1 and K2 are simultaneously operated in such manner that at small capacity values of K1, large values of K2 will be obtained and vice versa. The detuning of the frame circuit LC due to variation of the natural wave of the frame circuit K1 J1 is compensated by opposite variations of the circuit J2 K2. Both coils J1 and J2 are fixedly and preferably invariably coupled to the frame circuit.

In Fig. 4 the auxiliary antenna is variably coupled to the frame circuit III by means of an inductance. The detuning of the frame circuit caused by the variation of the coupling between auxiliary antenna and frame will be compensated by means of an auxiliary circuit III coupled to the frame circuit, and whose variable condenser K1 is so coupled to the coupling coil J2 that the natural wave of the auxiliary circuit is small when a fixed coupling exists between frame and auxiliary antenna or vice versa.

In a circuit according to Fig. 4 a variometer may be placed in series to coil J4 or a variable condenser in parallel or 'in series to coil J4. These circuit elements may be mechanically coupled with the tuning condenser C of the frame circuit so that at variation of the receiving frequency, the corrective action of the intermediate circuit will automatically so be changed that the detuning due to the auxiliary antenna will always be eliminated.

The application of the circuits is obviously not limited to direction finding receivers, but they can be employed in all cases which deal with the transmission of an alternating current with varying amplitude and direction to a tuned circuit by means of coupling, or where the degreeof coupling between two resonators is to be varied without displacement of the natural wave of the one circuit.

The condensers K in the circuits according to Figs. 1 and 2 may be readily replaced by a variable condenser adapted to the capacity of the auxiliary antenna and placed in parallel or in series to said auxiliary antenna.

I claim:

1. A receiver circuit for direction finding having a directional antenna and a linear auxiliary antenna in combination with means for suppressing reaction upon the directional antenna, said means comprising apparatus for varying the amount of energy transmitted from the auxiliary antenna to the directional antenna, an intermediate aperiodic circuit highly detuned with respect to the receiving waye connected to the directional antenna, a constant reactive coupling element interposedbetween said aperiodic circuit and said directional antenna and a variable reactive coupling element interposed between said aperiodic circuit and said auxiliary antenna.

2. A circuit according to claim l, and characterized in that the intermediate circuit'includes an inductance and at least one variable capacitance which in conformity with the coupling between the auxiliary antenna and the'intermediate circuit, are operative in such manner that-the wave resistance in the intermediate circuit remains constant independent of the value and the phase of the energy transmitted from the auxiliary antenna to the circuit of the directional antenna.

3. A circuit according to claim 1, characterized in that an adjustable balancing condenser is provided, said condenser being connected in circuit between said directional antenna and said auxiliary antenna and being so dimensioned that the resultant value obtained from its own capacity and the capacity of the auxiliary antenna is always constant with respect to the intermediate circuit.

4. A circuit according to claim 1, characterized in that the intermediate circuit consists of two parts, each having an inductance and a capacity,

and that the one capacity together withits associated inductance constitute means for varying the coupling between the auxiliary antenna and the directional antenna circuit, and that the other capacity together with its associated inductance constitute means for compensating the thereby produced detuning of the circuit of the directional antenna.

5. A circuit according to claim 1, characterized in that the auxiliary antenna and the intermediate circuit are coupled across an inductance in the circuit of the directional antenna.

WALTER 

